Valve positioner with overpressure protection capabilities

Abstract

A method of limiting control pressure provided to an actuator of a valve coupled to a valve positioner, a drive signal is provided to a pneumatic stage of the valve positioner. The pneumatic stage is arranged to control output pressure of the valve positioner in accordance with the drive signal. A pressure measurement from a pressure sensor communicatively coupled to the valve positioner is obtained, and an abnormal pressure is detected based on the pressure measurement. In response to detecting the abnormal pressure, the drive signal is controlled so as to limit the output pressure of the valve positioner, wherein the output pressure provides control pressure to the actuator.

The invention claimed is: 
     
       1. A method of limiting control pressure provided to an actuator of a valve coupled to a valve positioner, the method comprising:
 providing a drive signal to a pneumatic stage of the valve positioner, wherein the pneumatic stage is arranged to control output pressure of the valve positioner in accordance with the drive signal; 
 obtaining a pressure measurement from a pressure sensor communicatively coupled to the valve positioner; 
 detecting an abnormal pressure based on the pressure measurement; and 
 in response to detecting the abnormal pressure, controlling the drive signal so as to limit the output pressure of the valve positioner, wherein the output pressure provides control pressure to the actuator. 
 
     
     
       2. The method of  claim 1 , wherein the pressure sensor is configured to sense a level of a supply pressure provided to the valve positioner. 
     
     
       3. The method of  claim 1 , wherein the pressure sensor is configured to sense a level of the output pressure of the valve positioner. 
     
     
       4. The method of  claim 1 , wherein detecting the abnormal pressure comprises:
 comparing the pressure measurement to a predetermined threshold; and 
 determining that the pressure is abnormal when the measured pressure exceeds the predetermined threshold. 
 
     
     
       5. The method of  claim 1 , wherein the valve positioner includes a processor and a memory, and wherein detecting the abnormal pressure and controlling the drive signal comprises executing computer readable instructions stored in the memory. 
     
     
       6. The method of  claim 1 , wherein the valve positioner includes a control circuit configured to receive the pressure measurement, and wherein detecting the abnormal pressure and controlling the drive signal is performed by the control circuit. 
     
     
       7. The method of  claim 1 , wherein the drive signal is a current signal, and wherein controlling the drive signal comprises setting the drive signal to a value at or near zero milliamperes. 
     
     
       8. The method of  claim 1 , wherein the drive signal is a voltage signal, and wherein controlling the drive signal comprises setting the drive signal to a value at or near zero millivolts.